DE102011109071A1 - Pipe Forging Process with Urformed Hollow Block - Google Patents

Abstract

A method of forging a pipe, comprising the steps of: a. Feeding a hollow block (104) having a central recess (104a) to a radial forging apparatus, and b. Forging the hollow block (104) into a tube while reducing an outer diameter and a wall thickness of the hollow block (104), further comprising the step: a1. Producing the hollow block (104) with the central recess (104a) before step a. through a primary molding process.

Description

Method for forging a pipe

The invention relates to a method for forging a pipe according to the preamble of claim 1.

EP 1 814 679 A1 describes a method for producing a seamless hot-finished steel tube, in which a heated to a forming temperature block is formed by punching in a hollow block in a first forming step, wherein subsequently a finished tube is produced in the same heat in a second forming step by radial forging.

It is the object of the invention to provide a cost effective method for forging a pipe.

This object is achieved according to the invention for an initially mentioned method with the characterizing features of claim 1. By producing the hollow block with the central recess by a primary molding method, the hollow block is provided in a particularly simple and effective manner. In accordance with the principle of a primary forming, the block and the central recess required for forging the hollow block into a tube are formed in the same forming step, so that the outlay on the preparation of the hollow block is reduced.

Generally preferred, the invention relates to pipes made of an iron-based alloy, in particular steel, or even a nickel-based alloy or a titanium alloy.

In a first preferred embodiment of the invention, step a1 comprises an electroslag remelting process. For steels in particular, this provides an effective and universal method for the primary shaping of the hollow block.

Alternatively, the primary molding process may also include a centrifugal casting process. The centrifugal casting is particularly suitable for combination with a radial forging method, since a hollow block is already regularly produced with a central recess.

In a generally advantageous development of the invention, provision may be made for mechanical processing of the block to take place after step a1 and before step b in a step a2. Particularly advantageous, but not necessary, this may include the removal of a casting skin. It can be z. B. also to a homogenization of the recess, a deburring or any other suitable pre-treatment of the urgeformten hollow block prior to introduction into a radial forging device.

Generally, it is provided to carry out a heating of the hollow block after step a1 and before step b in a step a3 in order to achieve a defined forming temperature for the radial forging process. This may be particularly advantageous in alloys and structures that have a relatively narrow temperature range for forging machining.

Alternatively, it may be particularly advantageous to save energy and costs that between step a1 and step b no intermediate heating of the hollow block is made. In this case, therefore, the existing at the Urformung, regularly very high heat is used to obtain a temperature that is suitable for radial forging. In such a procedure, if necessary, a controlled cooling of the urgeformten hollow block before being introduced into the radial forging.

In a preferred embodiment of the invention, in a step a4, the desorbed hollow block is descaled before step b, preferably, but not necessarily, by a high-pressure process.

Further advantageously, it is provided that at least a portion of the recess of the hollow block is lubricated before step b by means of a lubricant. Such a lubricant may preferably be formed on the basis of glass and / or phosphate and / or graphite.

The step b of forging the hollow block into a tube while reducing an outer diameter and a wall thickness of the hollow block is generally advantageously carried out by means of a forging mandrel as an internal tool. In principle, open-die forging without a forging mandrel is conceivable, but the use of a forging mandrel is particularly effective. For the most part, the forging process will take place in such a way that the wall of the hollow block is pressed by external forging jaws against the forging mandrel arranged internally in the recess in order to effect the forming in the manner of a forging. The forging jaws can in particular be hydraulically driven, as a result of which a very controlled pressure curve is regularly achieved on the workpiece. Alternatively, however, another drive mechanism of the forging jaws may be provided, for. B. by falling weights or the like.

In a preferred embodiment, the forging mandrel has a coating that is particularly preferably, but not necessarily, has a scale coating, a ceramic coating and / or a coating with a metal alloy applied. These coatings can be submitted individually or in combination. Under a coated metal alloy and / or hard alloy as a coating, such coatings are to be understood, in the metal alloy and / or hard alloy incorporated hard materials, in particular ceramic nature, such as, for. As tungsten carbide or the like, have. Such coatings are often made by a thermal process such as plasma deposition welding, arc surfacing, or the like. The metal alloy serves to provide a sufficiently tough matrix which on the one hand provides a good and non-peeling connection with a substrate of the forging mandrel, in particular steel, and on the other hand achieves a correspondingly high hardness of the outwardly acting surface due to integrated hard material phases and / or hard material particles.

In a particularly preferred embodiment of the forging mandrel, it is provided that a main body of the forging mandrel has a surface profiling, wherein the coating is applied to the surface profiling. As a result, an additional positive connection is achieved in addition to a material flow, which particularly effectively prevents detachment of the coating from the base body. The profiling can be adapted to the shape and orientation particularly to the respective mechanical loads, z. B. to the forces caused by the respective forging jaws forces. In particular, the surface profilings form at least one undercut in an axial direction of the forging mandrel. As a result, a good fit is provided, which can also absorb very high forces acting in the direction of detachment of the coating. Particularly preferably, the surface profiling has a number of elevations and depressions on the surface of the base body.

The main body of a forging mandrel for use in a method according to the invention is preferably made of steel.

The coating of the forging mandrel protects advantageous against both thermal and mechanical loads. For example, the coating may have a targeted thermal conductivity to reduce a thermal effect on the body.

Generally, the coating can be applied by a thermo-chemical coating process.

In a generally advantageous development of a forging mandrel, internal cooling may additionally be provided, wherein the mandrel can be wetted with a coolant if required.

Further features and advantages of the invention will become apparent from the embodiment described below and in the dependent claims.

Hereinafter, a preferred embodiment of the invention will be described and explained in more detail with reference to the accompanying drawings.

1 shows a hot tool in the form of a radial forging mandrel in a side view.

2 shows the detail "Z" according to 1 for the not yet coated tool base.

3 shows the detail "Z" according to 1 for the now coated tool body.

4 shows the detail "Z" according to 1 for an alternative embodiment of the coated tool base.

5 shows a first micrograph for the item "Z" according to 1 through the hot tool; and

6 shows a second micrograph for the item "Z" according to 1 through the warm tool.

7 shows a schematic overall view of a radial forging.

• a. Zuführen eines Hohlblocks 104 mit einer zentralen Ausnehmung 104a zu einer Radialschmiedevorrichtung 101, und
• b. Schmieden des Hohlblocks 104 zu einem Rohr unter Verringerung des Außendurchmessers und der Wandstärke des Hohlblocks 104.

The method according to the invention for forging a tube preferably comprises the following steps:

• a. Feeding a hollow block 104 with a central recess 104a to a radial forging device 101 , and
• b. Forging the hollow block 104 to a tube reducing the outer diameter and the wall thickness of the hollow block 104 ,

Previously, according to the invention, in a step a1, the hollow block 104 along with its recess 104a produced in a primary molding process. This is preferably a centrifugal casting process or a remelting process, for example an electroslag remelting process.

After the original formation of the block 104 with the recess 104a if necessary, a mechanical reworking of the hollow block. This may be, for example, a descaling and / or a post-processing of the recess for Fine adjustment to a size and shape required for forging.

7 shows an example of a device for radial forging 101 at which the procedure can be carried out. Here is the block 104 end in a manipulator or holder 102 held. At the opposite end is a hot tool in the form of a blacksmith's mandrel 1 into the recess 104a introduced. At the height of the thorn 1 grab blacksmith jaws from the outside 103 on the hollow block to be processed 104 at. The blacksmith jaws 103 are preferred by means of hydraulic actuators with a defined pressure curve against the hollow block 104 pressed to a radially acting forging of the hollow block 104 to achieve a pipe. In an alternative embodiment, striking the forging jaws, z. B. via a cam mechanism may be provided.

The hollow block 104 can by means of the manipulator 102 rotated and / or moved axially.

It is understood that the method according to the invention can also be carried out on other radial forging devices.

In 1 is the mandrel or the hot tool 1 shown schematically in the form of a mandrel for producing a seamless tube. The shape may vary depending on requirements and in particular be cylindrical or slightly conical. The tool 1 has a tool base 2 on top of a workspace 3 has, which extends over a certain length in the direction of an axis a. In the workspace 3 is the tool 1 with a coating 4 provided the tool 1 protects against thermal or mechanical stress.

The whole in 1 shown tool body 2 represents within the meaning of the present invention, an exchangeable mandrel tip, for example, releasably on a mandrel body, for. B. in the form of a shaft 105 (please refer 7 ) of the radial forging mandrel 1 can be put on. Other embodiments or divisions of a replaceable spike tip 2 and a thorn body 105 are possible depending on requirements.

The exact structure of the tool as a detail in the "Z" according to 1 , ie as a section of the tool base body 2 is in the 2 and 3 shown. As can be seen, has the radially outer surface of the tool body 2 a surface profiling 5 on, consisting of a number of radially protruding elevations 6 exists between the thus resulting depressions 7 are arranged. The surveys 6 extend in the axial direction a by an amount B, which is preferably in the range of about 250 microns to 4000 microns. The height D of the surveys 6 opposite the wells 7 lies in a range of approx. 500 μm to 5,000 μm. The distance A between two surveys 7 is preferably in a range of about 200 microns to 2,000 microns.

The profiling 5 is doing so on the surface of the body 2 applied, that this is first processed smooth and then by machining the web-shaped in the radial section or rectangular recesses 7 incorporated, in particular screwed, be.

After this preprocessing, the surface of the tool base becomes 2 with a coating 4 provided as it is in 3 is shown. The total layer thickness C of the coating 4 fills the wells 7 and exceeds the height of the surveys 6 ,

Seen in the axial direction a, thus resulting for the material of the coating 4 as a result of surface profiling 5 an undercut, leaving the coating 4 when using the tool 1 very firmly on the body 2 liable.

In 4 is a preferred embodiment or to see solution. The pre-machining of the tool body 2 is analogous to the solution according to 2 and 3 made, ie it was first the surface profiling 5 into the smoothly machined tool body 2 brought in. The profile of the profiling corresponds to that according to 2 ,

Then, however, it was before applying the coating 4 first by using a thermo-chemical treatment process, a part of the material of the body 2 converted into a protective layer. The converted material 8th runs equidistant to the profiling 5 and is indicated by dashed lines. In doing so, the width of the elevations (webs) decreases correspondingly 6 and the depth of the cross-section again rectangular gaps, as it 4 shows.

On the converted material layer 8th That is, on the primary or inner protective layer produced by conversion of the carrier material during the conversion or subsequently the coating 4 applied as a second, outer layer, like it 4 for the finished tool shows. This is again done by a thermo-chemical process or for example by flame spraying or plasma spraying.

According to the in 4 shown solution is thus between the carrier material (body) 2 and the layer 4 a structure before or during application of the layer 4 on the carrier material 2 created in the converted material 8th manifests.

The representations in the 5 and 6 Examples of specific coatings can be found. The by transformation of the webs (elevations) 6 and filling gaps (recesses) 7 generated inner, more porous layer 8th and the second outer layer applied thereto 4 are easy to recognize. The inner layer 8th In the present case (converted material) consists of iron oxides and grows from the surface of the main body or the profiling. The gaps between the webs (elevations) are through the outer coating 4 filled (on).

In the embodiment according to 5 respectively. 6 the carrier material (tool base) was coated with iron oxides or material of the main body was converted into iron oxide. The carrier material is present steel. The maximum thickness of the coating on the base body is in this example about 1,000 microns.

The structured transition between the carrier material and the coating can be optimized depending on the application, so that complete peeling of the layer during use can be prevented. As a result, in particular the service life of the tool 1 be increased significantly.

The surfaces of the coated tools, before or during use by mechanical processing, eg. B. grinding and polishing (before use) or rolling (during use), smoothed.

The smoothing of the surface reduces the friction between the tool and the workpiece (rolling stock).

LIST OF REFERENCE NUMBERS

1

Hot tool or radial forging mandrel

2

Basic tool body

3

Workspace

4

coating

5

Surface profiling

6

survey

7

deepening

8th

converted material

101

Radial forging device

102

manipulator

103

forging jaws

104

block

104a

Recess in block

105

shaft

a

axially

B

length

D

height

A

distance

C

Total layer thickness

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• EP 1814679 A1 [0002]

Claims (15)

A method of forging a pipe, comprising the steps of: a. Feeding a hollow block ( 104 ) with a central recess ( 104a ) to a radial forging device, and b. Forging the hollow block ( 104 ) to a tube while reducing an outer diameter and a wall thickness of the hollow block ( 104 ), characterized by the step: a1. Making the hollow block ( 104 ) with the central recess ( 104a ) before step a. through a primary molding process. A method according to claim 1, characterized in that step a1 comprises an electroslag remelting process. A method according to claim 1, characterized in that step a1 comprises a centrifugal casting process. Method according to one of the preceding claims, characterized by the step a2. Mechanical processing of the hollow block ( 104 ) after step a1 and before step b; in particular comprising the removal of a casting skin. Method according to one of the preceding claims, characterized by the step a3. Heating the hollow block ( 104 ) after step a1 and before step b. Method according to one of claims 1 to 4, characterized in that between step a1 and step b no intermediate heating of the hollow block ( 104 ) is made. Method according to one of the preceding claims, characterized by the step a4. Descaling of the Urformed Hollow Block ( 104 ) before step b, in particular by a high pressure process. Method according to one of the preceding claims, characterized by the step a5. Lubricating at least a portion of the recess of the hollow block ( 104 ) before step b, in particular by means of a lubricant based on glass and / or phosphate and / or graphite. Method according to one of the preceding claims, characterized in that step b by means of a forging mandrel ( 1 ) is made as an internal tool. A method according to claim 9, characterized in that the forge ( 1 ) a coating ( 4 ), in particular comprising a scale coating, a ceramic coating and / or a coating with an applied metal alloy. A method according to claim 10, characterized in that a main body of the forging mandrel a surface profiling ( 5 ), wherein the coating ( 4 ) on the surface profiling ( 5 ) is applied. Method according to claim 11, characterized in that the surface profiling ( 5 ) in an axial direction of the forging mandrel ( 1 ) forms at least one undercut, the surface profiling ( 5 ), in particular a number of surveys ( 6 ) and depressions ( 7 ) has on the surface of the base body. A method according to claim 11 or 12, characterized in that the base body consists of steel. Method according to one of claims 11 to 13, characterized in that the coating ( 4 ) is a protective against thermal and mechanical stress layer. Method according to one of claims 11 to 14, characterized in that the coating ( 4 ) is applied by a thermo-chemical coating process.

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